Light emitting polymer electrical energy source

ABSTRACT

An electrical energy source is created by the combination of a light emitting polymer material having at least one light emitting surface emitting light energy of a specified frequency bandwidth and a photovoltaic cell having a light collecting surface and a pair of electrical contacts. The light collecting surface of the photovoltaic cell is optically coupled with the light emitting surface of the light emitting polymer material. An open-circuit voltage is generated between the pair of electrical contacts as a result of the absorption of emitted light energy from the light emitting polymer material by the photovoltaic cell. In the preferred embodiment, the light emitting polymer is a tritiated organic polymer to which at least one organic phosphor or scintillant is bonded. Maximum absorption of the emitted light energy is achieved by the intimate optical contact between the light emitting surface and the light collecting surface, by matching the maximum absorption frequency bandwidth of the photovoltaic cell with the specified frequency bandwidth of the emitted light energy from the light emitting polymer material, and by the structural arrangement of the light emitting polymer material itself.

TECHNICAL FIELD

The present invention pertains to the generation of electrical energythrough the combination of a light source and a photovoltaic cell. Inparticular, this invention pertains to a long-life, electrical energysource generated by the combination of a radioisotope activated polymermaterial emitting a low level of light with a photovoltaic cell arrangedin intimate optical contact with the light emitting polymer material,the light emitting polymer in the preferred embodiment being comprisedof a tritiated organic polymer to which an organic phosphor orscintillant is bonded.

BACKGROUND ART

Various types of energy sources consisting of photocells activated bysome type of nuclear radiation are known in the prior art. Thesedevices, sometimes referred to as "nuclear batteries" or "atomicbatteries", convert nuclear electromagnetic radiation into electricalenergy by one of two methods, single conversion systems or doubleconversion systems. Single conversion nuclear batteries generateelectrical energy by converting the nuclear radiation (i.e. alphaparticles, beta particles or gamma radiation) into electrical energy bydirect absorption of the nuclear radiation at the p-n junction of asemiconductor material, for example, U.S. Pat. Nos. 3,094,634 and3,304,445. Double conversion nuclear batteries generate electricalenergy by converting the nuclear radiation into electromagneticradiation, usually by irradiating a phosphorescent material that willgenerate light in the visible spectrum, and then converting thatelectromagnetic radiation into electrical energy by absorbtion of theelectromagnetic radiation at the p-n junction of a semiconductormaterial, usually a typical photovoltaic cell, for example, U.S. Pat.Nos. 3,031,519, 3,053,927, and 3,483,040.

While the concept of a nuclear battery is not new, a practical andcommercially feasible device of this type has not been possible becauseof the extreme dangers involved in the handling and use of radioactivematerials. Most nuclear batteries of the type known in the prior arthave either been unsafe or have required such extensive shielding of thenuclear material used to power the battery that the device is renderedimpractical for most applications. The regulatory standards forradiation leakage upon container failure impose additional constraintsthat limit the applications for such devices. One possible means ofovercoming these safety limitations is to limit the amount ofradioactive material used in such a device. For example, in a typicalsmoke detector a small amount of radioactive foil containing onemicrocurie of radioactive Americium 241 is used to power the detectioncircuit of the device. In general, regulatory standards allow for smallamounts of radioactive material to be used under certain circumstances.For example, with proper shielding and packaging, a device containing 5curies of radioactive material may be approved by the Nuclear RegulatoryCommission for limited commerical activities. These low limits onradioactive material effectively limit the radiation energy, and hence,the electrical energy that may be generated from any such source.

Using the amount of radioactivity as measured in curies, the totalamount of power available from such an energy source can be calculated.Each curie of radioactive material will produce 3.7×10¹⁰ Beqerels(decays)/second. Assuming that the radioactive emission is in the formof a beta particle from the radioisotope tritium having an average 5.6KeV of energy, the total theoretical power emitted is 32.5microwatts/curie. Theoretically, if there were a complete conversion ofall of the power of this nuclear radiation to electrical energy, thetotal amount of power available from a small, but safe, amount ofradioactive material containing less than 25 curies of tritium would beless than 1 milliwatt. Though the total amount of power generated bysuch a device over the half life of the tritium radioactive material maybe on the order of a hundred watt-hours, until recently relatively fewapplications could operate with a continuous power supply outputting inthe microwatt range. With the advent of CMOS and other low powercircuitry, however, applications and uses for this type of long-life,low-watthour power supply are now becoming more practical.

Although a variety of self-luminous, low light sources have beenavailable for a long time (e.g. radium and tritium activated phosphorsused for creating self-luminous paints for watch dials, etc., U.S. Pat.Nos. 3,033,797, 3,325,420 and 3,342,743), it has generally been regardedthat such materials were unsuitable for commercial use for theconversion of light into electricity. The low levels of radioactivityassociated with such materials, though generally not harmful ordangerous, do not provide an adequate source of power for the nuclearbatteries of the type known in the prior art. In addition to the lowlight level (50 micro-lamberts or less), such sources may also becharacterized by rapid and unpredictable light decay and, in the case ofradium-activated light sources, may produce undesirable radiationhazards associated with their decay products.

Though the concept of a long-life, electrical energy source activated bya radioactive material is attractive and has many potential applicationsnone of the prior art devices have been able to create a safe, yetsufficiently powerful, energy source that is commercially feasible.Accordingly, there is a continuing need to develop a safe and practicallong-life, electrical energy source powered by a radioactive source.

SUMMARY OF THE INVENTION

In accordance with the present invention, an electrical energy source iscreated by the combination of a light emitting polymer material havingat least one light emitting surface emitting light energy of a specifiedfrequency bandwidth and a photovaltaic cell having a light collectingsurface and a pair of electrical contacts. The light collecting surfaceof the photovoltaic cell is optically coupled with the light emittingsurface of the light emitting polymer material. An open-circuit voltageis generated between the pair of electrical contacts as a result of theabsorption of emitted light energy from the light emitting polymermaterial by the photovoltaic cell.

In the preferred embodiment of the present invention, the light emittingpolymer is a tritiated organic polymer to which at least one organicphosphor or scintillant is bonded. Maximum absorption of the emittedlight energy is achieved by the intimate optical contact between thelight emitting surface and the light collecting surface, by matching themaximum absorption frequency bandwidth of the photovoltaic cell with thespecified frequency bandwidth of the emitted light energy from the lightemitting polymer material, and by the structural arrangement of thelight emitting polymer material itself. To maximize the surface areabetween the light emitting polymer and the photovoltaic cell, the lightemitting surface and the light collecting surface are preferablyarranged so that they are generally parallel to and in intimate contactwith each other. In addition, the light emitting polymer material andthe photovoltaic cell may be arranged to allow the photovoltaic cell tobe constructed in manner so as to absorb light energy at more than asingle surface.

In another embodiment of the present invention, the light emittingpolymer material is optically separated from the photovoltaic cell by anoptical control means. for controlling the amount of light that may passthrough the optical control means to be absorbed by the photovoltaiccell. The optical control means may be a liquid crystal display (LCD) orlead lantium zirconium titinate (PZLT) or similar material that iseither transparent or opaque, depending upon the voltage or currentapplied to the material. By controlling the amount of light that may beabsorbed by the photovoltaic cell, the optical control means alsocontrols the output of the photovoltaic cell and, hence, operates aseither a voltage or current regulator, depending upon the particularcircuit that utilizes the electrical energy source of the presentinvention. The optical control means allows the electrical energy sourceof the present invention to simulate an alternating current source froma direct current source without the need for electrical circuitryexternal to the electrical energy source.

The present invention provides a novel radioisotope-activated,electrical energy source that exhibits several desirablecharacteristics. Foremost, the electrical energy source of the presentinvention is relatively safe and is, thus, viable for general commercialuse when the quantities of radioactivity are generally below 100 curies.The low emissivity and high energy density of the preferred embodimentutilizing a tritiated organic polymer to which an organic phosphor orscintillant is bonded enable the electrical energy source torealistically utilize 4.0% or more of the theoretical 3.6 amp-hours ofelectrical energy that are present in each curie of tritium. In thisembodiment, an electrical energy source having 100 curies of tritium iscapable of providing 1 microwatt of power at 1 volt and 1 microamp forthe entire lifetime of the electrical energy source, approximately 20years.

Because the electrical energy generated by the present invention isdependent upon the rate of emission of photons from the light emittingpolymer (which is in turn dependent upon the rate of beta-emissions fromthe radioisotope used to activate the light emitting polymer), theamount of energy available is constant and determinable. In addition toproviding a unique source of electrical energy for CMOS, NMOS and otherlow power types of electronic circuitry, the output stability of theelectrical energy source of the present invention makes it ideallysuited for applications that require a very constant source of power andensure that it is not drained of its energy if subjected to ashort-circuit. Moreover, the materials and packaging of the presentinvention can be selected to enable the electrical energy source tooperate in a cryogenic environment without significant degradation ofthe power compared to conventional chemical batteries, because the rateof conversion of the photons by the photovoltaic cell is positivelyaffected by decreasing temperature.

Although light emitting polymers have been available for a number ofyears for various uses (primarily as self-luminescent paints), it is notknown to use such light emitting polymers to power electrical energysources. The present invention has discovered their usefulness for thispurpose and, more importantly, the adaptability of light emittingpolymers as compared to other prior art radioisotope vehicles to permitthe design of electrical energy sources with greater efficiency andsafety than in prior art devices.

Accordingly, a primary objective of the present invention is to providea safe, yet sufficiently powerful, long-life, radioisotope-poweredelectrical energy source that is commercially feasible.

Another objective of the present invention is to provide a long-lifesource of electrical energy by the combination of aradioisotope-activated, light emitting polymer and a photovoltaic cell.

A further objective of the present invention is to provide an electricalenergy source wherein the conversion efficiency by a photovoltaic cellof light emitted by a light emitting polymer is maximized.

An additional objective of the present invention is to provide anelectrical energy source that includes an optical control means forcontrolling the amount of electrical energy generated by controlling theamount of light that is received by the photovoltaic cell from a lightsource.

A still further objective of the present invention is to provide along-life, electrical energy source that provides a consistent poweroutput by generating electrical energy at a constant watt-hour rate.

These and other objectives of the present invention will become apparentwith reference to the drawings, the detailed description of thepreferred embodiment and the appended claims.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cut-away pictorial view of a light emitting polymerelectrical energy source in accordance with the preferred embodiment ofthe present invention.

FIG. 2 is a graph showing the spectral emissions of a various phosphorsused as scintillators in the light emitting polymer.

FIG. 3 is a graph showing the relative scintillation efficiencies foreach of the phosphors shown in FIG. 2.

FIG. 4 is a graph showing the maximum theoretical conversionefficiencies for various semiconductor materials.

FIG. 5 is a graph showing the collection efficiency of a photovoltaiccell as a function of the wavelength of the incident light.

FIG. 6 is a pictorial view showing a multiple-layer configuration of analternative embodiment of the present invention arranged to allow fordual-sided utilization of the photovoltaic cells.

FIG. 7 is a pictorial view of an alternative embodiment of the presentinvention showing the light emitting polymer and the photovoltaic cellin spiral jelly-roll configuration.

FIG. 8 is a pictorial view of an alternative embodiment of the presentinvention showing the light emitting polymer cast about the photovoltaiccell in a spherical arrangement.

FIG. 9 is a shcematic view showing another alternative embodiment of thepresent invention including an optical control means.

FIG. 10 is a circuit diagram of the electrical energy source of thepresent invention showing the addition of other circuit elements.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention is directed to a safe and practical, long-life,electrical energy source made by the combination of a light emittingpolymer, activated by a radioisotope source, with a photovoltaic cell,to produce electrical energy. As will be appreciated, the potentialvariations of such a combination are numerous. The practical feasibilityof an electrical energy source in accordance with the present inventiondepends upon a number of considerations, including: (a) the choice of asuitable long-lived radioisotope, (b) the efficiency of thescintillation process in the polymer, (c) the efficiency of thephotovoltaic cell, (d) radiation damage to the polymer and thephotovoltaic cell, (e) the optical mating of the polymer and thephotovoltaic cell, and (f) the geometry of the polymer and thephotovoltaic cell. Each of these considerations will be discussed indescribing the preferred embodiment of the present invention. It will beobserved that the use of a light emitting polymer provides anopportunity to effectively design a safe and practical, long-lifeelectrical energy source in response to these considerations.

Referring now to FIG. 1, a cut-away pictorial representation of thepreferred embodiment of the present invention is shown. The electricalenergy source 10 is comprised of a planar sheet of light emittingpolymer ("LEP") material 12 that is interposed between a pair ofphotovoltaic cells 14 and 16 having planar dimensions similar to the LEPmaterial 12. The photovoltaic cells 14 and 16 the LEP material 12 areencased in a sealed case 18, preferably a laser-welded, stainless steelcase, having a pair of electrical contacts 20 and 22 exposed on one endof the case 18. The contacts 20 and 22 are disposed in a pair of ceramicinsulators 24 and 26 and are connected to the photovoltaic cells 14 and16 in such a manner that connected to the photovoltaic cells 14 and 16in such a manner that one of the contacts will provide a positivevoltage potential and the other contact will provide a negative voltagepotential.

In the preferred embodiment, the LEP material 12 is a tritiated organicpolymer to which an organic phosphor or scintillant is bonded. Such anLEP material was obtained from Amersham International plc, AmershamPlace, Little Chalfont, Buckinghamshire, England, and pending NRCregulatory approval, may be available from Amersham International plc.It should be recognized that other types of LEP material known in theprior art may also be utilized with the present invention. (e.g., U.S.Pat. Nos. 3,033,797, 3,325,420 and 3,342,743). Those aspects of the LEPmaterial 12 that allow it to be used effectively in the presentinvention are discussed below in connection with the various designconsiderations set forth above.

In the preferred embodiment, the photovoltaic cells 14 and 16 areamorphous thin-film silicon solar cells, Model No. 035-01581-01,available from ARCO Solar, Inc., Chatsworth, Calif., or theirequivalent. These cells have their highest efficiency conversion(greater than 20%) in the blue range of the spectrum of visible light tomatch the frequency bandwidth of the emitted light of LEP materialincorporating a phosphor that emits in the blue range. While theparticular photovoltaic cells 14 and 16 in the preferred embodiment havebeen selected to match the blue range of the spectrum of visible light,it should be apparent that other photovoltaic cells may be selected tomatch the bandwidth of light emitted at other frequencies. Inparticular, as discussed below, it is known that a new solar cell, knownas the Sunceram II (trademark), available from Panasonic's IndustrialBattery Sales Div., is claimed to more efficient than conventionalamorphous silicon solar cells, especially in the red range of thespectrum of visible light.

To maximize the optical transfer between the LEP material 12 and thephotovoltaic cells 14 and 16, the surfaces of the photovoltaic cells 14and 16 not in contact with the LEP material 12 are coated with areflective material, preferably an aluminum paint or equivalent. Theedges of the LEP material 12 not in contact with the photovoltaic cells14 and 16 are clad with a similar reflective material. The surfaces ofthe LEP material 12 and the photovoltaic cells 14 and 16 that abut oneanother are coated with a contact gel, Rheogel 210C., available fromSynthetic Technology Corp., McLain, Va., or its equivalent, as a meansfor optically coupling the surfaces to increase the amount of light thatis transmitted from the LEP material 12 to the photovoltaic cells 14 and16.

SELECTION OF THE RADIOISOTOPE

The radioisotope that is used in the LEP material 12 must producesufficient scintillations in the LEP material to insure an adequateproduction of light for absorption by the photovoltaic cells 14 and 16.For safety purposes, it is desirable that the selected radioisotope bechemically bonded to the polymer. By chemically bonding the radioisotopeto the polymer, any undesirable build-up of the radioisotope isprevented and the concentration levels of the radioisotope will remainconstant no matter what environmental factors the LEP material 12 issubjected to. Unlike radioisotopes in a liquid or gaseous state, thebonding of the radioisotope to the polymer in the LEP material 12 of thepresent invention prevents the free release of radiation if the materialor container is ever broken. The bonding of the radioisotope to theorganic polymer is expected to result in NRC approval for the use ofhigher allowable levels of radioactive material for radioisotopes inthis format.

The radioisotope should have a half-life comparable to the desireduseful lifetime of the electrical energy source 10. Because the power isdirectly proportional to the rate of decay of the radioisotope in theLEP material 12, for a given desired power output the rate of decayshould ideally correspond to the power requirements of the electricalenergy source 10. If the half-life is too long with respect to theuseful life of the electrical energy source 10, then the amount ofradioisotope required to produce the same rate of decay is increased,thus presenting increased safety and shielding problems. If thehalf-life is too short with respect to the useful life of the electricalenergy source 10, then the amount of radioisotope required to producethe desired rate of decay at the end of the useful life of theelectrical energy source requires that the LEP material 12 be overloadedinitially, thus generating wasted energy at the beginning of the life ofthe device. Obviously, if a decaying power source is desired oracceptable this consideration is not important.

To minimize the radiation hazards associated with use of a radioisotope,the radiation emitted by the selected radioisotope should not be verypenetrating. Preferably, a high percentage of the radiation emitted bythe radioisotope should be absorbed by the photovoltaic cells 14 and 16or by the sealed case 18. Therefore, radioisotopes emitting gammaradiation or high-energy x-rays are not preferred; beta radiationemitters are preferred. In addition, the radioisotope must be selectedso that it may be chemically bonded to the organic polymer to achievethe desired solid, captured state for the LEP material 12. A furtherconsideration in selecting the radioisotope is the economic cost of theradioisotope. The cost of producing various radioisotopes varies byorders of magnitude. For example, the cost per curie of ¹⁴ C is morethan two orders of magnitude greater than for ³ H.

Table I provides data on several radioisotopes, among others, that maybe used with the electrical energy source 10 of the present invention.

                  TABLE I    ______________________________________    Radioisotope .sup.3 H  .sup.14 C                                  .sup.10 Be                                         .sup.32 Si                                              .sup.32 P    ______________________________________    Half-life    12.3      5730   2.7 × 10.sup.6                                         650  .039    (years)    Max. beta Energy                 .0186     .156   .555   .22  1.71    (Me V)    Ave. beta Energy                 .0056     .049   .194   .065 .68    (Me V)    Mass of 1 curie                 1.0 × 10.sup.-4                           .22    75     .058 NA    (grams)    Absorber to stop beats                 .72       24     180    30   790    (mg/cm.sup.2)    Power Density                 320       1.3    .015   76    (mW/g)    ______________________________________

For the safety reasons mentioned above, beta-active radioisotopes areespecially preferred in practicing the present invention. The decay ofbeta-active isotopes results in a continuum of beta energies beingemitted from the radioisotope. This continuum extends from zero up to amaximum value as shown in Table I. The average beta energy is computedusing the equation:

    <E>=0.099E(1-Z.sup.0.5)(3+E.sup.0.6)

where <E> is the average energy in MeV, E is the maximum energy in MeV,and Z is the atomic number of the daughter nucleus that results afterthe decay. The first three radioisotopes in Table I decay to stableelements, but ³² Si decays to ³² P, which in turn decays to stablesulphur. Therefore, the decay for each ³² Si atom produces the combinedbeta energy of the decay of both the silicon and the phosphorous.

One curie is defined to be 3.7×10¹⁰ decays/second. The mass of theradioisotope required to produce this activity is obtained from thefollowing equation:

    m=2.8×10.sup.-6 (T.sub.1/2)M

where T_(1/2) is the half-life of the radioisotope expressed in yearsand M is the atomic mass.

Because the radioisotope is an internal component of the polymer, agiven thickness of shielding must be provided around theradioisotope-activated polymer to completely absorb all of the betaradiation. The following range relation was used to compute the requiredabsorber thickness in Table I:

    R=(540E-130(1-e.sup.-4E))

where R is in mg/cm² and E, the maximum beta energy, is in MeV. In orderto obtain the linear thickness required by the absorber to shield allbeta radiation, one would divide R by the density of the absorber. Forexample, if a polymer of 2 g/cm³ is used as the absorber surrounding theLEP material 12, then the required thickness for ³ H would be 0.0036 mm.

Based upon the considerations set forth above and especially for safetyreasons, the preferred radioisotope for the present invention istritium. With a halflife of 12.36 years and a beta decay with an 0.0186MeV maximum energy, tritium has been considered one of the mostinnocuous of fission produced radioisotopes. Because of the low energyand penetration power of the beta particle associated with its decay,tritium does not pose a significant external radiation hazard. The betaparticles emitted by tritium are not even capable of penetrating theepidermis. In addition, the chemical bonding of the tritium in the solidpolymer form prevents escape of the tritium in its gaseous state,thereby decreasing the chance that tritium may be absorbed into the bodyby skin penetration in the form of a gas or vapor.

Another method to compare the various radioisotopes is to compare theirrelative power densities, the decay power produced per gram of material.With the greatest power density/gram and the least amount of absorbentmaterial necessary to stop all beta particles from being emitted,tritium is the best choice for an electrical energy source that providesa low power, long-life electrical energy source when the requirements ofa single electrical energy source are less than 5 to 10 milliwatts-hoursfor the desired lifetime of the electrical energy source, approximately20 years or less.

It will be seen that if a higher power output or longer lifetime of theelectrical energy source is required, other radioisotopes may beutilized in the light emitting polymer, depending upon the environmentaland safety considerations involved. The next most favorable radioisotopemay be the ³² Si and ³² P combination, although the shieldingrequirements for this radioisotope would be significantly increased.Because silicon is similar to carbon, it should be readily incorporatedinto the polymer. Although ¹⁴ C also appears to be a good candidate foruse as the radioisotope, it should be recognized that the long half-lifewill require about 250 times as much ¹⁴ C in the polymer as compared to³ H to produce the same power. For example, in a military or spaceapplication, ¹⁴ C or the ³² Si and ³² P combination may be preferredbecause of the higher energy of the beta particles and because of thesignificantly longer half-life, provided that adequate shielding can beincorporated into the packaging of the electrical energy source tocompensate for the higher energy radiation and the increased curie levelrequired by the longer half-life radioisotopes.

SCINTILLATION EFFICIENCIES

As a beta particle generated by the selected radioisotope moves throughthe organic polymer, energy is released by several mechanisms: (a)excitation of π-electrons to excited states, (b) π-electron ionization,(c) excitation of other electrons to excited states, and (d) ionizationof other electrons. All but the first of these mechanisms ultimatelyonly result in an increased thermal energy within the LEP material 12.Only the first results in scintillation, the release of a photon fromthe organic phosphor or scintillant upon decay from the excited state.For many organic materials, this occurs with a probability of about 10%.Therefore, only about 10-20% of the energy deposited by a beta particleis available for light production. Because it may be necessary to shiftthe light produced by such scintillations into the portion of thespectrum to which the photovoltaic cells 14 and 16 are more sensitive,secondary and tertiary phosphors may also need to be added to the LEPmaterial 12. This may result in further degradation of the scintillationefficiency of the LEP material 12. For a more detailed explanation ofthe operation of scintillators in response to beta radiation, referenceis made to E. Schrafm, Organic Scintillator Detectors, 1973, pp. 67-74,which is hereby incorporated by reference herein.

In the LEP material 12 of the preferred embodiment, the scintillationefficiency is increased by bringing the primary organic phosphor into aweak bonding with the tritiated organic polymer. Because the betaparticle emitted by the tritium is of such low energy, the closer thetritium is located to the phosphor, the greater the probability that thebeta particle will be able to interact with the phosphor. Because theaverage mean distance of the path of an emitted beta particle is lessthan 1 micron, the probabilities of interaction between the betaparticle and the phosphor decrease dramatically unless the phosphor islocated within that range.

In the preferred embodiment, the LEP material 12 utilizes both a primaryand a secondary phosphor. The primary organic phosphor may be anyphosphor or scintillant in the groups PPO, PBD, or POPOP that operatesto capture the beta particle and emit a photon in the ultravioletfrequency. The secondary phosphor may either be bonded to or admixedwith the organic polymer and performs a Stokes shift on the emittedphoton to shift its frequency to the desired frequency of the light tobe emitted by the LEP material 12. The various techniques for performinga Stokes shift are well known in the art.

Unlike the prior art techniques of admixing the tritium with thephosphor or encapsulating gaseous tritium in a glass vessel, the LEPmaterial 12 utilized by the present invention maximizes thescintillation efficiency of the beta particle and the organic phosphorby positing the tritium relatively near the primary phosphor and byarranging the LEP material 12 such that it is generally opticallytransparent at the desired frequency of the emitted light. In addition,to minimize any optical blockage of photons emitted by the LEP material12, it desirable that the catalysts for bonding both the radioisotopeand the phosphor or scintillant be completely removed or disappear afterthe polymerization process.

Referring now to FIG. 2, the spectral emissions of a blue phosphor and ayellow-green phosphor used as the secondary phosphor in the LEP material12 are shown. FIG. 3 shows the relative scintillation efficiencies as afunction of output voltages over various curie levels in the LEPmaterial 12 utilizing each of these phosphors. As can be seen, therelative efficiency of the yellow-green phosphor decreases withincreasing levels of the radioisotope. This effect, known as bleaching,is well known in the field of scintillation. Obviously, it is desirablethat the phosphor(s) selected for use with the LEP material 12 shouldnot be subject to bleaching or other types of deterioration as a resultof activation by the particular radioisotope selected for use in the LEPmaterial 12.

It should be noted that although the preferred embodiments are describedin terms of scintillants that emit energy in the visible spectrum, it isalso possible to use a scintillant that emits electromagnetic energy inthe ultraviolet, infrared, or other frequency bands of theelectromagnetic spectrum. accordingly, the term "light" as used in thisapplication is intended to encompass all frequencies of electromagneticradiation produced by scintillation activity. For example, if theaverage mean path of a photon emitted in the ultraviolet spectrum by theprimary phosphor is sufficiently great to escape the polymer, and if aphotovoltaic cell capable of absorbing energy having a wavelength of 400nm or less were available, the LEP material 12 might not need asecondary phosphor and the energy emitted by the primary phosphor couldbe used directly to power the photovoltaic cells 14 and 16. In addition,the bandwidth of the emitted light from the LEP material 12 need not belimited to monochromatic light. Various combinations of primary and/orsecondary phosphors in the LEP material could be used to broaden thebandwidth of either or both the intermediary or emitted energy from theLEP material 12. Again, the polymer structure of the LEP material allowsthe LEP material 12 to be designed to achieve these objectives.

PHOTOVOLTAIC CELL EFFICIENCIES

Presently, most of the work, both theoretical and practical, on thedesign of semiconductor photovoltaic cells relates to their use as solarcells that are designed to absorb all of the spectral energy availablefrom the sun, either at AM0 conditions outside the earth's atmosphere,or at AM1 conditions at sea level. It is well known that there are boththeoretical and practical efficiency limits for such solar cells. Intheory, there are only two parameters that will determine the efficiencyof a solar cell, the band gap energy of the solar cell material and thetemperature of the cell. For an amorphous silicon solar cell, thebandgap energy of 1.1 eV means that only those photons of wavelengthsless than about 1,100 nm are capable of producing electron-hole pairs inthe photovoltaic cells that will result in the generation of electricalenergy; the remaining energy is lost, usually in the form of heat.Referring now to FIG. 4, the maximum theoretical conversion efficienciesfor a variety of photovoltaic cell materials are shown as a function oftemperature and energy gap.

In practice, there are a number of other factors that limit theconversion efficiency of solar cells, including the excess energy lossfor photons that are within the band gap energy, the fill factor lossand the voltage loss as a result of the mismatch of the impedance of theload and the source. The net result is that typical solar cellefficiencies of only 20% are generally achievable to date. Recently,greater efficiencies have been achieved for a printed compound thin-filmphotovoltaic cell utilizing the group II-VI compound semiconductorsCdS/CdTe. These solar cells, known as the Sunceram II, are availablefrom Panasonic's Industrial Battery Sales Div., Secaucus, N.J., andutilize an n-layer (CdS) and a p-layer (CdTe) semiconductor filmscreated by a film-fabrications process that entails paste application byscreen printing and sintering in a belt-type furnace. The Sunceram IIsolar cells have an output five times higher than conventional amorphoussilicon solar cells when illuminated by tungsten light.

In the present invention, the design parameters of the photovoltaic celldo not have to be matched to the entire bandwidth of visible light tooptimize absorption of the entire solar spectrum. Rather, the design ofthe photovoltaic cells 14 and 16 may be tailored to the particularbandwidth and wavelengths of emitted light from the LEP material 12. Itis well known that different semiconductor materials have differentbandgap energies and, hence, will absorb photons of differentwavelengths (e.g., Si absorbs photons with λ<1.1 μm and GaAs absorbsphotons with λ<0.9 μm). However, the wavelength of the photon alsodetermines where in the p-n junction the photons will be converted intoelectron-hole pairs. For short wavelengths (λ=0.55 μm), most photonswill be converted into electron-hole pairs in a narrow region near thesurface of the p-layer of the p-n junction. Whereas, at longerwavelengths (λ=0.9 μm), the absorption coefficient for the semiconductoris small and absorption takes place mostly in the n-layer of the p-njunction. FIG. 5 shows the collection efficiency for both the p-layerand the n-layer of a photovoltaic cell as a function of the wavelengthof the incident light. The collection efficiency of the photovoltaiccell will be influenced by the minority-carrier diffusion length of thesemiconductor material and by the absorption coefficient. A largeabsorption coefficient leads to heavy absorption near the surface of thep-n junction, resulting in strong collection in the skin layer. A smallabsorption coefficient allows deep penetration of photons so the baselayer of the p-n junction becomes more important in carrier collection.A typical GaAs photovoltaic cell produces more of the skin layer effect,and a typical Si photovoltaic cell produces more of the base layereffect. For a more detailed discussion as to the effect of wavelengthand semiconductor selection on the conversion efficiencies of thephotovoltaic cell, reference is made to Edward S. Yang, Fundamentals ofSemiconductor Devices, pp. 147-162 (1978).

In the present invention, the selection of the primary and secondaryphosphors of the LEP material 12 can be made to generate a monochromaticor a narrow bandwidth of emitted light, the frequency of which can bematched to the particular type of photovoltaic cell 14 and 16 desired.This matching depends upon the type of conversion desired (base vs. skineffect), the efficiency of the semiconductor material in the bandwidth,and other considerations relating to the design of the electrical energysource 10, including the curie loading, safety factors, the cost, andthe environment in which the device will be operated. Although such adevice is not currently available, it may be possible to provide adouble-sided, monochromatic, bandwidth-matched photovoltaic cell for usewith light emitting polymer in the present invention that could achieveconversion efficiencies of 60-70% or higher.

POLYMER AND PHOTOVOLTAIC CELL RADIATION DAMAGE

The long term performance of a polymer scintillator can be affected bythe accumulated radiation dose deposited in the polymer. In addition, avariety of other factors can affect the aging of the polymer. The majorvariable in pure polymer aging are: (a) radiation intensity andwavelength distribution; (b) ambient temperature; (c) monomer content;(d) level of other impurities; and (e) oxygen concentration in thesurrounding atmosphere. To increase the life of the polymer, the lastfour factors should all be minimized. For the LEP material 12, fouradditional factors affect the stability and aging of the polymer: (f)radiation resistance and purity of the scintillators used; (g)wavelength of the emitted light (the higher the better); (h) presence ofmultiple tritium labelled molecules (the lower the better), and (i)radioactive concentration level of the polymer. The basic polymer of theLEP material 12 of the preferred embodiment is known to have one of thelowest coefficients of radiation damage of any polymer.

As for the photovoltaic cells, it is well known that radiation energiesin excess of 4 KeV can damage the p-n junction in the semiconductormaterial. If the single conversion process taught by the prior art wereused to produce electrical energy, the damage to one cm² of a p-njunction caused by the beta particles emitted by a one curie of tritiumwould effectively destroy the p-n junction in a relatively short amountof time. In addition, if a single conversion process were used, thepolymer containing the tritium could be no more than 1 micron thick,otherwise the polymer itself would prevent the beta particles fromreaching the p-n junction. The present invention allows a doubleconversion process to be used with a low-level light source and stillachieve a conversion efficiency that is equal to or greater than theconversion efficiencies achieved by single conversion processes. Byefficiently converting the beta particles to photons in the LEP material12, the present invention simultaneously solves the problems ofradiation damage and the distance that the p-n junction can be locatedfrom the energy source. An additional advantage of utilizing the LEPmaterial 12 of the present invention is that the LEP material 12 itselfshields the p-n junction of the semiconductor material of thephotovoltaic cells 14 and 16 from radiation damage, thereby increasingthe useful life of the electrical energy source 10.

OPTICAL MATING CONSIDERATIONS

To maximize the transfer of light emitted by the LEP material 12, theLEP material 12 must be efficiently coupled to the photovoltaic cells 14and 16. This is achieved by the use of a means for optically couplingthe LEP material 12 with the photovoltaic cells 14 and 16 and bycreating smooth surfaces on both the LEP material 12 and thephotovoltaic cells 14 and 16.

The primary purpose of the means for optically coupling the LEP material12 and the photovoltaic cells 14 and 16 is to insure that as much of thelight that is emitted by the LEP material 12 will be allowed to passthrough to the light collecting surface of the photovoltaic cells 14 and16. Unlike prior art devices, the means for optically coupling the twomaterials is not required to also serve as a means for isolating the twomaterials. In one embodiment, an anti-reflective coating matched to thefrequency of the emitted light and the indices of refraction of the twomaterials is used as the means for optically coupling the two materials.Where the index of refraction of the polymer is n_(p) and the index ofrefraction of the photovoltaic cell is n_(c), then the index ofrefraction of the anti-reflective coating should be the:

    n.sub.r =(n.sub.p n.sub.c).sup.0.5

The index of refraction of silicon is about 3.5 and the index ofrefraction for most polymers is around 1.5. Thus, the anti-reflectivecoating should have an index of refraction of about 2.3. The thicknessof the anti-reflective coating should be 1/4 wavelength of the frequencyof the emitted light. A similar effect may also be achieved by the useof an optical coupling gel, such as Rheogel 210C. or its equivalent. Aswith the geometrical considerations to be discussed below, the effect onefficiency of the means for optically coupling the two materials mayvary depending upon the materials selected and the manner of theirconstruction.

The light emitting surface of the LEP material 12 and the lightcollecting surfaces of the photovoltaic cells 14 and 16 should be assmooth as possible to aid in the transmission of light between the two.The existence of a rough interface between the two surfaces will alterthe angles of incidence of the various light rays emitted by the LEPmaterial 12 and could allow some of the light rays to be reflected backinto the polymer, thereby lengthening their optical path and reducingthe probability that they will be re-reflected back into thephotovoltaic cells 14 and 16.

It should also be noted that the use of optical concentrators in theoptical mating between the LEP material 12 and the photovoltaic cells 14and 16 could also be used to increase the optical efficiency of theconversion process.

GEOMETRICAL CONSIDERATIONS

The preferred method of constructing the LEP material 12 and thephotovoltaic cells 14 and 16 is in the planar format shown in FIG. 1. Interms of optical efficiency, the geometrical shape of the LEP material12 and the photovoltaic cells 14 and 16 will determine, to a certainextent, how much of the emitted light is actually received by thephotovoltaic cells 14 and 16. In the planar embodiment shown in FIG. 1,there is a loss of emitted light from the edges of the LEP material 12not in contact with the photovoltaic cells 14 and 16. For a sheet of LEPmaterial 12 having dimensions of 42 mm×13 mm×0.5 mm, there would be aloss of emitted light of approximately 5% due to the optical aperture ofφ_(critical) along the edges of the LEP material 12. This can bedemonstrated by calculating the optimum numerical aperture based uponthe indices of refraction for each material using Snell's law. This losscan be minimized by cladding the edges of the LEP material with areflective coating in a manner similar to that known in the fiber opticfield; however, the cladding will not achieve the optimum total internalreflection and some of the energy may be still absorbed or lost throughthe edges of the LEP material 12. Another advantage of the planarembodiment of the present invention is in maximizing the relative amountof surface area available between the LEP material 12 and thephotovoltaic cells 14 and 16. The amount of power output available fromthe photovoltaic cells 14 and 16 is a direct function of the totalsurface area available for the light collecting surface. In addition, ifthe thickness of the LEP material is kept small, 0.5 mm, the averagemean path of the photons emitted is not consumed by the thickness of theLEP material itself.

In an alternative embodiment shown in FIG. 6, the LEP material 32 isarranged with a double-sided photovoltaic cell 34 in a multiple-layeredconfiguration. In this embodiment the efficiency of the electricalenergy source 30 is increased because the emitted light may be absorbedby more than a single photovoltaic cell. In addition, the photovoltaiccell 34 is capable of receiving light from both sides, as well as anylight that may have passed through adjacent photovoltaic cells. Thephotovoltaic cell 34 could be a photovoltaic laminate, for example,constructed of a first semiconductor layer, a first conductive substratelayer, a dielectric isolation layer, a second conductive substratelayer, and a second semiconductor layer. Using the screening techniquereferred to above for the Sunceram II, the photovoltaic cell 34 mightalso be constructed as a three-part photovoltaic laminate comprising:semiconductor, dielectric, and semiconductor, with the conductive layerbeing overlayed by a screening process.

In another embodiment shown in FIG. 7, the LEP material 42 is arrangedwith a double-sided photovoltaic cell 44 in a jelly-roll spiralconfiguration. In this embodiment the efficiency of the electricalenergy source 40 is increased because of the minimum amount of edgesurface relative to the light emitting and light absorbing surfaces ofthe LEP material 42 and the photovoltaic cell 44. One possiblephotovoltaic cell for this embodiment may be a new flexiblephotoelectric material developed by 3M, Minneapolis, Minn., inconnection with the center for Amorphous Semiconductors at Iowa StateUniversity, Ames, Iowa. The top and bottom of the electrical energysource 40 may also be provided with circular photovoltaic cells (notshown) to further increase the efficiency by capturing any emitted lightfrom the edges of the LEP material 42.

In still another embodiment shown in FIG. 8, the LEP material 52 actsboth as the light source for the photovoltaic cell 54 and the structuralsupport for the electrical energy source 50. In this embodiment, the LEPmaterial 52 is cast in the form of a sphere surrounding the photovoltaiccell 54. The photovoltaic cell 54 would also preferably be in the formof a sphere having a screened conductor around the periphery of thesphere. The LEP material 52 could be coated with a reflective material,such as aluminum, thereby insuring total internal reflection of all ofthe emitted light from the LEP material 52. Each of these sphericalcells could be encased in an inactive polymer structure that would serveas the shielding and support for multiple cells for the electricalenergy source 50.

It will be apparent that the use of the LEP material 12 as the carrierfor the selected radioisotope provides the present invention withnumerous advantages in terms of the geometrical and designconsiderations for constructing the electrical energy source 10.Although only a limited number of possible design combinations of theLEP material 12 and the photovoltaic cells 14 and 16 (or singlephotovoltaic cell or double-sided photovoltaic cell) have beenpresented, it should be appreciated that many other designs will bepossible because of the nature of the LEP material 12.

OPTICAL CONTROL MEANS

In still another embodiment of the present invention shown in FIGS. 9and 10, the LEP material 60 is optically separated from the photovoltaiccells 62 by an optical control means 64 for controlling the amount oflight that may be absorbed by the photovoltaic cells 62. The opticalcontrol means 64 may be a liquid crystal display (LCD) or lead lantiumzirconium titinate (PZLT) or similar material that is either transparentor opaque, depending upon the voltage or current applied to thematerial. By controlling the amount of light that may be absorbed by thephotovoltaic cells 62, the optical control means 64 also controls theoutput of the photovoltaic cells 62 and, hence, operates as either avoltage or current regulator depending upon the particular circuit thatutilizes the electrical energy source of the present invention. Theinclusion of the optical control means 64 allows the electrical energysource of the present invention to simulate an alternating currentsource from a direct current source without the need for any electricalcircuitry external to the electrical energy source.

It will be readily apparent that other circuit elements may beincorporated with the electrical energy source 10 of the presentinvention to optimize the electrical energy source for a particularapplication. As shown in FIG. 10, a zener diode 76 has been added toestablish a fixed voltage level for the output of the electrical energysource 70 having LEP material 72 emitting light energy to be aborbed bythe photovoltaic cells 74. A capacitor 78 has also been added to act asan internal electrical storage device that would be charged up to apredetermined voltage level over a given time period and then utilizedto power the desired circuit for a relatively shorter time period, afterwhich the electrical energy source 70 would recharge the capacitor 74for the next demand period. In this way, the large amp-hour power of theelectrical energy source 70 may be realized in applications where anintermittent power demand is required, but the demand is higher than thesteady state power (either current or voltage) supplied by theelectrical energy source 70. For example, if the electrical energysource 70 were used to power a telemetry detection/transmission circuit,such a circuit could be designed to have the detection portion run offthe steady state power of the electrical energy source, with thetransmission portion of the circuit powered for short durations by thecapacitor 74.

ELECTRICAL CONSIDERATIONS

Not only is the electrical energy source 10 of the present inventionunique as a battery because of its relatively long-life, otherelectrical characteristics of the electrical energy source 10 of thepresent invention make it particularly well-suited for certainapplications. Based upon the test data reported in Tables II and IIIbelow, the internal impedance of the the electrical energy sources inaccordance with the present invention is calculated at approximately 5MOhms. This high impedance is particularly desirable for low-powerapplications, such as CMOS and NMOS devices. Because the impedance ofthe load is easily matched to the impedance of the source, it is easierto achieve the maximum output from the electrical energy source of thepresent invention. The nature of the source of the electrical energy ofthe present invention, namely a generally constant rate of radioactivedecay, allows the electrical energy source 10 to be short circuitedwithout causing any damage to the device and, more importantly, withoutaffecting the power available in the device at some time in the future.Unlike low-power chemical batteries, the electrical energy source of thepresent invention does not release all of its "stored" energy when it isshort circuited. This means that there is no risk of explosion or damageto the device as a result of the short circuit. Also, when the shortcircuit is removed from the electrical energy source 10, the output ofthe device is immediately restored to its pre-short state. This allowsthe electrical energy source 10 to easily act as an ideal constantvoltage source, even after the source has been short circuited.

SAMPLE RESULTS

The following tables set forth the measured voltage output of thecircuit shown in FIG. 10 having a single electrical energy source inaccordance with the present invention and utilizing both the blue andyellow-green phosphors for various curie levels. The LEP material wasplaced in intimate physical and optical contact with a single speciallycalibrated photovoltaic cell Model No. 035-015817-01, available fromARCO Solar, Inc., having dimensions of 38×17 mm. The measured voltagesare measured in millivolts in parallel with a 10M ohm input impedence ofthe volt meter used to take the measurements:

                                      TABLE II    __________________________________________________________________________    Blue Phosphor               1 Ci/g 5 Ci/g 25 Ci/g                                    50 Ci/g    Dimensions 45 × 15 × 1                      41 × 15 × 1                             47 × 15 × 1                                    48 × 15 × 1    Total curies           (mm)               0.62   2.7    15     34    __________________________________________________________________________    Load        1K     0.00   0.05   0.15   0.3    (ohms)        4.7K   0.1    0.1    0.7    1.3        10K    0.1    0.2    1.3    2.6        22K    0.2    0.6    3.0    6.1        47K    0.3    1.1    5.8    2.0        68K    0.5    1.6    8.8    18.1        100K   0.75   2.4    13.1   27.1        150K   1.05   3.5    18.7   38.6        220K   1.5    4.9    26.6   54.7        330K   2.3    7.9    42.7   88.3        470K   3.0    10.1   54.7   112.7        680K   4.6    15.4   83.4   171.6        1M     5.9    19.8   107.1  220        2.2M   11.4   38.3   206    421        4.7M   20.4   68.3   365    727        10M    29.4   97.9   516    984    Output Voltages (millivolts)    __________________________________________________________________________

                                      TABLE III    __________________________________________________________________________    Yellow-Green Phosphor               1 Ci/g 5 Ci/g 25 Ci/g                                    50 Ci/g    Dimensions 35 × 15 × 1                      47 × 15 × 1                             55 × 15 × 1                                    49 × 15 × 1    Total curies           (mm)               0.46   2.83   13.7   31.6    __________________________________________________________________________    Load        1K     0.00   0.0    0.1    0.1    (ohms)        4.7K   0.00   0.1    0.3    0.4        10K    0.0    0.2    0.7    0.8        22K    0.1    0.5    1.6    1.9        47K    0.2    0.8    3.1    3.8        68K    0.2    1.3    4.6    5.7        100K   0.3    1.9    6.9    8.4        150K   0.45   2.7    9.9    12.1        220K   0.65   3.8    14.0   17.1        330K   1.05   6.1    22.5   27.6        470K   1.25   7.9    28.7   35.2        680K   2.0    12.1   43.8   53.7        1M     2.5    15.5   56.3   68.9        2.2M   4.9    29.9   108.4  132.5        4.7M   8.7    52.9   190.7  233        10M    12.4   75.9   271.0  330    Output Voltages (millivolts)    __________________________________________________________________________

Although the description of the preferred embodiment has been presented,it is contemplated that various changes could be made without deviatingfrom the spirit of the present invention. Accordingly, it is intendedthat the scope of the present invention be dictated by the appendedclaims rather than by the description of the preferred embodiment.

We claim:
 1. An electrical energy source, comprising:a light emittingpolymer material having at least one light emitting surface emittinglight energy in a specified frequency bandwidth, the light emittingpolymer material comprising an organic polymer incorporating aradioisotope emitting beta particles to which an organic phosphor isbonded, wherein the radioisotope consists of a radioisotope selectedfrom the group ³ H, ¹⁰ Be, ¹⁴ C, ³² Si and ³² P; and a photovoltaic cellhaving a light collecting surface and a pair of electrical contacts, thelight collecting surface of the photovoltaic cell being substantiallyintimately optically coupled to the light emitting surface of the lightemitting polymer, such that an open-circuit voltage is generated betweenthe pair of electrical contacts as a result of the photovoltaic cell'sabsorption of light energy emitted from the light emitting polymer. 2.The electrical energy source of claim 1 wherein the light emittingpolymer material is comprised of a tritiated organic polymer to which anorganic phosphor is bonded.
 3. The electrical energy source of claim 2wherein the organic phosphor is comprised of a primary organic phosphorfor absorbing a beta particle emitted by the tritiated organic polymerand emitting photons at a first frequency bandwidth and a secondaryorganic phosphor for shifting the frequency bandwidth of the photonsemitted by the primary organic phosphor to establish the specifiedfrequency banwidth for the light energy emitted by the light emittingpolymer material.
 4. The electrical energy source of claim 3 wherein theprimary organic phosphor consists of a phosphor from the group PPO, PBD,and POPOP.
 5. The electrical energy source of claim 1 wherein the numberof curies of the radioisotope present in the light emitting polymermaterial is less than 100 curies/gram.
 6. The electrical energy sourceof claim 1 wherein the half-life of the radioisotope activating thelight emitting polymer material is approximately the same as the averagedesired lifetime of the electrical energy source.
 7. The electricalenergy source of claim 1 wherein the photovoltaic cell has a maximumabsorption value at a specified frequency bandwidth that is matched tothe specified frequency bandwidth of the emitted light energy of thelight emitting polymer material.
 8. The electrical energy source ofclaim 1 wherein the specified frequency bandwidth of the emitted lightenergy of the light emitting polymer is substantially monochromatic. 9.The electrical energy source of claim 1 wherein the light emittingsurface of the light emitting polymer material and the light collectingsurface of the photovoltaic cell are generally parallel to one another.10. The electrical energy source of claim 1 wherein the light emittingsurface of the light emitting polymer material and the light collectingsurface of the photovoltaic cell are generally planar.
 11. Theelectrical energy source of claim 1 wherein the total energy produced bythe electrical energy source is less than 200 milliwatts.
 12. Theelectrical energy source of claim 1 wherein the average useful life ofthe electrical energy source is at least 10 years.
 13. The electricalenergy source of claim 1 wherein at least 75% of the light emittingsurface is in optical contact with the light collecting surface.
 14. Theelectrical energy source of claim 1 further including means foroptically coupling the light emitting surface of the light emittingpolymer material with the light collecting surface of the photovoltaiccell.
 15. The electrical energy source of claim 14 wherein the means foroptically coupling the light emitting surface and the light collectingsurface comprises an anti-reflective coating, the index of refraction ofwhich is substantially equal to the square root of the product of theindex of refraction of the light emitting polymer material and the indexof refraction of the photovoltaic cell.
 16. The electrical energy sourceof claim 15 wherein the means for optically coupling the light emittingsurface and the light collecting surface is a contact gel.
 17. Theelectrical energy source of claim 1 further comprising concentratingmeans operably interposed between the light emitting surface of thelight emitting polymer material and the light collecting surface of thephotovoltaic cell for concentrating the emitted light energy that isreceived by the photovoltaic cell.
 18. The electrical energy source ofclaim 1 further comprising a zener diode electrically connected betweenthe pair of electrical contacts.
 19. The electrical energy source ofclaim 1 further comprising a capacitor electrically connected betweenthe pair of electrical contacts.
 20. The electrical energy source ofclaim 1 wherein the light emitting polymer material emits light energyfrom both a first and second light emitting surface.
 21. The electricalenergy source of claim 20 further comprising a second photovoltaic cellhaving a second light collecting surface and a second pair of electricalcontacts, the second light collecting surface of the second photovoltaiccell being optically coupled to the second light emitting surface of thelight emitting polymer material.
 22. The electrical energy source ofclaim 21 wherein the first and second pair of electrical contacts arearranged in parallel electrical connection.
 23. The electrical energysource of claim 21 wherein the first and second pair of electricalcontacts are arranged in series electrical connection.
 24. Theelectrical energy source of claim 1 wherein the light emitting polymermaterial and the photovoltaic cell are both planar and coiled togetherto form a spiral structure having the light emitting surface of thelight emitting polymer material operably adjacent the light collectingsurface of the photovoltaic cell.
 25. The electrical energy source ofclaim 1 wherein the light emitting polymer material and the photovoltaiccell are concentric spheres having the light emitting surface of thelight emitting polymer material operably adjacent the light collectingsurface of the photovoltaic cell.
 26. An electrical energy sourcecomprising:a plurality of planar sheets of light emitting polymermaterial that each emit light energy in a specified frequency bandwidthfrom each of a first and second planar surfaces of each sheet, the lightemitting polymer material comprising an organic polymer incorporating aradioisotope emitting beta particles to which an organic phosphor isbonded, wherein the radioisotope consists of a radioisotope selectedfrom the group ³ H, ¹⁰ Be, ¹⁴ C, ³² Si and ³² P; and a plurality ofplanar sheets of photovoltaic laminate, including in successive planarorientation:a first layer of semiconducting material; a first layer ofconductive substrate; a layer of dielectric material a second layer ofsemiconducting material; and a second layer of conductive substrate, andfurther including:a first pair of electrical contacts operably connectedto the first layer of conductive substrate; and a second pair ofelectrical contacts operably connected to the first layer of conductivesubstrate, the sheets of light emitting polymer material and the sheetsof photovoltaic laminate being alternately arranged together to form alayered planar structure with at least a portion of the first lightemitting surface of one of the sheets of light emitting polymer materialoptically coupled to the first layer of semiconducting material of afirst sheet of photovoltaic laminate and at least a portion of thesecond light emitting surface of the same sheet of light emittingpolymer material optically coupled to the second layer of semiconductingmaterial of a second sheet of photovoltaic laminate, such that anopen-circuit voltage is generated between the both the first and thesecond pair of electrical contacts as a result of the absorption ofemitted light energy from the sheet of light emitting polymer materialby the first and second sheets of photovoltaic laminate.
 27. Theelectrical energy source of claim 26 wherein the first and second pairof electrical contacts are arranged in parallel electrical connection.28. The electrical energy source of claim 26 wherein the first andsecond pair of electrical contacts are arranged in series electricalconnection.
 29. An electrical energy source comprising:a light emittingpolymer material that emits light energy in a specified frequencybandwidth from each of a first and second planar surfaces of the lightemitting polymer material, the light emitting polymer materialcomprising an organic polymer incorporating a radioisotope emitting betaparticles to which an organic phosphor is bonded, wherein theradioisotope consists of a radioisotope selected from the group ³ H,¹⁰Be,¹⁴ C,³² Si and ³² P; and a planar photovoltaic laminate, including insuccessive planar orientation:a first layer of semiconducting material;a first layer of conductive substrate; a layer of dielectric material asecond layer of semiconducting material; and a second layer ofconductive substrate, and further including:a first pair of electricalcontacts operably connected to the first layer of conductive substrate;and a second pair of electrical contacts operably connected to the firstlayer of conductive substrate, the light emitting polymer material andthe photovoltaic laminate being coiled together to form a spiraledcylindrical structure with at least a portion of the first lightemitting surface of the light emitting polymer material opticallycoupled to the first layer of semiconducting material and at least aportion of the second light emitting surface of the light emittingpolymer material optically coupled to the second layer of semiconductingmaterial of the photovoltaic laminate, such that an open-circuit voltageis generated between the both the first and the second pair ofelectrical contacts as a result of the absorption of emitted lightenergy from the light emitting polymer material by the photovoltaiclaminate.
 30. The electrical energy source of claim 29 wherein the firstand second pair of electrical contacts are arranged in parallelelectrical connection.
 31. The electrical energy source of claim 29wherein the first and second pair of electrical contacts are arranged inseries electrical connection.
 32. The electrical energy source of claim26 wherein the light emitting polymer material is comprised of atritiated organic polymer to which an organic phosphor is bonded. 33.The electrical energy source of claim 26 wherein the photovoltaiclaminate has a maximum absorption value at a specified frequencybandwidth that is matched to the specified frequency bandwidth of theemitted light energy of the light emitting polymer material.
 34. Theelectrical energy source of claim 33 wherein the specified frequencybandwidth of the emitted light energy of the light emitting polymer issubstantially monochromatic.
 35. The electrical energy source of claim29 wherein the light emitting polymer material is comprised of atritiated organic polymer to which an organic phosphor is bonded. 36.The electrical energy source of claim 29 wherein the photovoltaiclaminate has a maximum absorption value at a specified frequencybandwidth that is matched to the specified frequency bandwidth of theemitted light energy of the light emitting polymer material.
 37. Theelectrical energy source of claim 29 wherein the specified frequencybandwidth of the emitted light energy of the light emitting polymer issubstantially monochromatic.
 38. An active electrical element,comprising:a light emitting polymer material having at least one lightemitting surface emitting light energy in a specified frequencybandwidth, the light emitting polymer material comprising an organicpolymer incorporating a radioisotope emitting beta particles to which anorganic phosphor is bonded, wherein the radioisotope consists of aradioisotope selected from the group ³ H, ¹⁰ Be, ¹⁴ C, ³² Si and ³² P; aphotovoltaic cell having a light collecting surface and a pair ofelectrical contacts, the light collecting surface of the photovoltaiccell being optically coupled to the light emitting surface of the lightemitting polymer; and optical control means intimately interposedbetween the light emitting surface of the light emitting polymermaterial and the light collecting surface of the photovoltaic cell forcontrolling the amount of emitted light energy that may be absorbed bythe photovoltaic cell, such that an open-circuit voltage is generatedbetween the pair of electrical contacts as a result of the photovoltaiccell's absorption of light energy emitted from the light emittingpolymer when the optical control means allows at least a minimum amountof the emitted light energy to be absorbed by the photovoltaic cell. 39.The electrical energy source of claim 38 wherein the optical controlmeans is a liquid crystal display material.
 40. The electrical energysource of claim 38 wherein the optical control means is a lead lantiumzirconium titinate material.
 41. The electrical energy source of claim38 wherein the light emitting polymer material is comprised of atritiated organic polymer to which an organic phosphor is bonded. 42.The electrical energy source of claim 38 wherein the photovoltaic cellhas a maximum absorption value at a specified frequency bandwidth thatis matched to the specified frequency bandwidth of the emitted lightenergy of the light emitting polymer material.
 43. The electrical energysource of claim 42 wherein the specified frequency bandwidth of theemitted light energy of the light emitting polymer is substantiallymonochromatic.